Cluster Flies
Order:
Diptera
Family:
Calliphoridae
Scientific Name: Pollenia rudis
The
cluster fly, Pollenia rudis,
is widely distributed in North America and Europe, located wherever the
earthworm, its host, is found.
The common name of this species represents its gregarious behavior
of gathering in clusters before hibernation.
One by one they will enter a building in early fall to seek shelter
from cooling temperatures.
Soon, a “cluster” of adult flies accumulates in wall voids and
dark corners, under shelving, beneath curtains, and in other protective
areas.
When the weather warms, the cluster flies emerge from their hiding
places and exit the building.
Their presence in large numbers is often annoying to the building’s
occupants.
Biology and Habits
The adult cluster fly is slightly larger than the house fly, about 3/8 inch (8mm) long. Its robust body is dark gray, nonmetallic, and covered by short golden hairs. The abdomen exhibits light and dark patches of color. The venation of the membranous wings is also an important identification characteristic.
Adult
cluster flies may be found around flowering plants and trees.
Mating occurs outdoors, and fertilized females will deposit their
eggs in cracks in the soil.
After egg-hatch, the developing maggot parasitizes an earthworm
be entering its body cavity.
Complete metamorphosis from egg to adult generally occurs within
27 to 39 days.
Four generations of cluster flies may occur annually.
Control
Initiate control tactics for cluster flies before they enter buildings in large numbers. Sealing exterior cracks and holes requires a thorough inspections of a structure to pinpoint the entry points. This work should be done in mid-summer. Repellents can be applied to exterior surfaces in the late summer or early fall to discourage adult flies from landing on a structure. Check with local extension offices to find out when the sightings of adult cluster flies are typically reported. Control by disrupting the life cycle cannot be aimed at the immature maggot because its parasitic host – the earthworm – is an important ecological component of the community.
Once the flies have settled in wall voids and other secluded areas, control is difficult to achieve. Moreover, secondary pests such as beetles and rodents, which feed on dead flies, may cause a secondary infestation.
For temporary indoor relief, remove adult flies with a vacuum cleaner, or use space sprays and insect light traps. To prevent reentry in the interior rooms involved, seal the possible entry routes such as around window pulleys, electrical outlets, switch boxes, and window and door frames.
Care
must be taken when treating occupied areas with insecticides.
Check the label for specific instructions regarding treatment sites
of the target pest.
(Courtesy of the National Pest Control Association.)